Does a "painting wall" in

the backyard sound like a good idea?
My nephew-in-law thinks it is. He has attached a child-height "wall" to one fence in their back garden where his children can "paint". They can go out there and make a glorious mess of water-poster colour on this wall - there and nowhere else. If they want to save the pictures then someone takes a photograph. 
The wall gets used frequently. Visiting children love it too. It is always carefully explained that this is a special painting wall and that is the only place that it is all right to use paint. His children understand the concept of "graffiti". 
They also paint indoors of course - when they are indoors. Their backyard is built to play in. There is a vegetable garden but, apart from that there is an above ground pool (with security fencing and adult only gate features). There is a sand pit and a tree house (you climb six feet up the ladder to get there), bars to swing on, a swing attached to a tree and paths for riding on.
If it is not actually raining you are likely to find the children outside. They have no problems entertaining themselves there.
Even inside they seem to have no problems entertaining themselves. They just get on with it. Of course they also watch the occasional bit of television but cuddling up to someone for a story is much preferred.
Yes, they have far more toys than we had as children but they do not have nearly as many as their cousins. My nephew's children appear to have a vast number of toys but no similar outdoor play area. Their backyard is designed for ease of maintenance. There is  no vegetable garden or even a sandpit. It's understandable if both parents work long hours and are not of the same practical bent. 
Even with all the toys they have my nephew's children are much less able to entertain themselves. Their play can be quite imaginative but they expect constant adult involvement in what they are doing.
The contrast between the two families is stark. The Senior Cat was commenting on this after my brother and his wife left. It also made me think. I am the one who buys the books we give them as presents - books being easy to post and something we believe to be very important. The odd thing is that I am already buying books which are distinctly different for the two families - or I think I am. This time I gave my brother a book to take back for the eldest child in the backyard family. It is a book filled with activity. The children in it are out and about and doing things.
It is not a book I would have contemplated for her slightly older cousin. I am a little disturbed by this. As children we spent most of our time outside - even if we took our books out there to read. We would all have loved a book filled with action - and just about any other book as well. 
I need to review my book choosing habits. Perhaps the non-active child needs some action to spur her on?